Poly(arylene thioether) (hereinafter abbreviated as "PATE") represented by poly(p-phenylene sulfide) is known as a polymer having a high crystalline melting point and excellent in heat resistance, solvent resistance and mechanical properties.
However, PATE, which is an aromatic polymer, is restricted in its application to uses for which flexibility is required due to its high crystalline melting point and glass transition temperature, or involves a drawback to its development into fields used as a solution due to its high solvent resistance. Therefore, it has been strongly desired to improve the above-described problems while retaining the good heat resistance of PATE.
The present inventors started an investigation with a view toward providing improved A-A copolymers by introducing an alkylene thioether component, which has aliphatic recurring units, in the arylene thioether component constituting PATE.
First of all, the present inventors repeatedly carried out an investigation with a view toward reacting a dihalogen-substituted aromatic compound forming an arylene thioether component and a dihalogen-substituted aliphatic compound forming an alkylene thioether component together with an alkali metal sulfide in a polar organic solvent, thereby preparing a copolymer. It was however impossible to prepare an A-A copolymer having the intended properties and a uniform composition.
This is believed to be based on the following reason. The dihalogen-substituted aromatic compound is different from the dihalogen-substituted aliphatic compound in reactivity and stability to the alkali metal sulfide. It is therefore difficult for them to undergo a copolymerization reaction under the same reaction conditions. Namely, the dihalogen-substituted aliphatic compound exhibits good reactivity to the alkali metal sulfide under relatively mild conditions as to polymerization temperature (for example, about 200.degree. C. or lower), while the dihalogen-substituted aromatic compound is stable under the same conditions and scarcely reacts with the alkali metal sulfide. On the other hand, the dihalogen-substituted aromatic compound shows good reactivity under conditions higher than such a temperature (for example, higher than 200.degree. C.), while the dihalogen-substituted aliphatic compound becomes liable to decompose under such conditions. It is therefore difficult to conduct a copolymerization reaction in either case.
The present inventors previously found that when an alkali metal sulfide is caused to act on PATE in a polar organic solvent, the principal chain of PATE is cut to depolymerize PATE, whereby a compound having at least one alkali thiolate group can be obtained (Japanese Patent Application Laid-Open No. 7334/1992 and U.S. Pat. application Ser. No. 07/686,972, abandoned). This process according to the depolymerization features that a compound having an alkali thiolate group, which is a group rich in reactivity, can be formed in a desired form by optionally adjusting its average polymerization degree to any level ranging from oligomers to polymers relatively high in molecular weight. In addition, it is expectable to provide a copolymer having a uniform composition when using a compound, which has a relatively low average polymerization degree of about 50 or lower and has been obtained by this depolymerization process, as a copolymerizing component with other components because the molecular weight distribution of this compound is relatively even.
The present inventors continued the investigation with a view toward forming an A-A copolymer by using a compound obtained by this depolymerization process as an arylene thioether component and a dihalogen-substituted aliphatic compound as an alkylene thioether component to copolymerize them.
By the way, it is disclosed in Japanese Patent Application Laid-Open No. 48727/1987 to add a polyhalogenated aliphatic compound at an optional stage of polymerization upon producing a poly(arylene thioether) by the reaction of a dihalogenated aromatic compound with an alkali metal sulfide in a polar organic solvent, thereby obtaining the poly(arylene thioether) as a polymer high in melt crystallization temperature. In Japanese Patent Application Laid-Open No. 247228/1990, there is also disclosed a process for the production of a polymer by reacting a dihalogen-substituted aromatic compound with a dihalogen-substituted aliphatic compound. However, these processes do not relate to the production process of copolymers in which an alkali thiolate-containing compound obtained by the depolymerization of PATE is used.
On the other hand, it is disclosed in Japanese Patent Application Laid-Open No. 140233/1990 to react a poly(phenylene sulfide) with an alkali metal sulfide at 150.degree.-230.degree. C. in a polar aprotic solvent, thereby producing a poly(phenylene sulfide) having a thiolate or thiol group on at least one terminal thereof. However, this polymer is not a polymer obtained by depolymerization. In addition, it is only disclosed that the polymer is used for forming a graft polymer which serves as a compatibilizer by melting it to mix with various kinds of polymers.
As another production process of an arylene thioether polymer, it has been proposed to react a dihalogen-substituted aromatic compound with an aromatic dithiol or an alkali metal salt thereof (alkali thiolate) (Japanese Patent Publication Nos. 19713/1970 and 4398/1971, Japanese Patent Application Laid-Open Nos. 197634/1986, 200127/1986, 529/1987, 530/1987, 91530/1987 and 20530/1987, etc.). However, these production processes relate to the production process of polymers in which aromatic compounds are used, but do not relate to the production process of A-A copolymers wherein a dihalogen-substituted aliphatic compound is used as a copolymerizing component.